Accidental Poisoning Kills 27 Horses at Texas Boarding Barn

Twenty-seven horses died the week of July 16 from apparent accidental poisoning at a boarding farm in College Station, Texas.

Researchers at nearby Texas A&M University (TAMU) suspect a pesticide fumigant used in a feed silo nearby was responsible for the deaths. However, the reason for the extreme reaction to the chemical is still unknown.

"We did identify phosphine in the stomach cavities of three of the horses," said Richard Adams, DVM, PhD, dean of TAMU's College of Veterinary Medicine. "And since that is the product of the pesticide that the stable was using, the logical conclusion is that it was the cause."

Adams said the results of preliminary tests showed no evidence of anything wrong with the feed itself.

The first 24 horses died within 12 hours of each other. Five were hospitalized at TAMU. Three of those horses died, and veterinarians performed necropsies on the animals.

"Some metabolites of the gas can cause liver damage, though we have not seen any evidence of that as yet," Adams said. "We have no way of knowing the actual dose received by those that remain alive."

Catherine Barr, PhD, ABT, a veterinary toxicologist with the Texas Veterinary Diagnostic Laboratory, explained that aluminum phosphide is used as a fumigant. The solid phosphide produces phosphine as a gas when exposed to water, including water droplets in the air and in the feed itself, Barr said.

The phosphine was found in the horse's stomach contents--not the lungs--suggesting it was ingested rather than inhaled.

Phosphide is a highly controlled substance, due to its high toxicity. A pesticide applicator's license is required for its purchase and use.

The Texas Department of Agriculture's Pesticide Division said it is necessary to aerate treated commodities for a minimum of 48 hours prior to feeding it to horses.

Farm owner Bradley Raphel said Carousel Acres had used the same grain treatment for the past eight years, with no previous problems.

The Texas Department of Agriculture is currently investigating the method of fumigant application used at the farm.